Methods for improving uplink coverage, throughput and transmission latency are currently being investigated in third generation partnership project (3GPP) in the context of the Release 6 (R6) universal mobile telecommunications system (UMTS) study item “FDD uplink enhancements”.
It is widely anticipated that in order to achieve these goals, Node-B (base station) will take over the responsibility of scheduling and assigning uplink resources (physical channels) to users. The principle is that Node-B can make more efficient decisions and manage uplink radio resources on a short-term basis better than the radio network controller (RNC), even if the RNC retains coarse overall control. A similar approach has already been adopted in the downlink for Release 5 (R5) high speed downlink packet access (HSDPA) in both UMTS FDD and TDD modes.
It is also envisioned there could be several independent uplink transmissions processed between a wireless transmit/receive unit (WTRU) and a universal terrestrial radio access network (UTRAN) within a common time interval. One example of this would be medium access control (MAC) layer hybrid automatic repeat request (HARQ) or simply MAC layer automatic repeat request (ARQ) operation where each individual transmission may require a different number of retransmissions to be successfully received by UTRAN. To limit the impact on system architecture, it is expected that protocol layers above the MAC should not be affected by introduction of the enhanced uplink dedicated channel (EU-DCH). One requirement that is introduced by this is the in-sequence data delivery to the radio link control (RLC) protocol layer. Therefore, similar to HSDPA operation in the downlink, a UTRAN re-ordering function is needed to organize the received data blocks according to the sequence generated by the WTRU RLC entity.
A soft handover macro-diversity operation requires centralized control of uplink transmissions in each cell within an active set. The active set may include a plurality of Node-Bs. Retransmissions are generated until successful transmission is realized by at least one of the Node-Bs. Successful transmission is not guaranteed at all of the Node-Bs. Therefore, since a complete set of successful transmissions may not be available within any one Node-B, re-ordering of successful transmissions cannot be accomplished.